Method for producing a resist structure

ABSTRACT

High resolution resist structures with steep edges are obtained using standard equipment, with high sensitivity, particularly in the deep UV range. A photoresist layer consisting of a polymer having anhydride groups and blocked imide- or phenolic hydroxyl groups and of a photoactive component which forms a strong acid during irradiation is first deposited on a substrate, followed by irradiation with a patterned image. The irradiated photoresist layer is then treated with a water-based or a water-alcohol-based solution of a polyfunctional amino- or hydroxy-siloxane, and is etched in an oxygen-containing plasma.

Background of the Invention

The present invention relates to a method for producing high resolutionresist structures with steep edges.

The production of resist structures plays an important role inmicroelectronics. For example photoresists are structured usingphotolithographic means in the manufacture of semiconductor components.One consequence of the recent advances in microelectronics, however, isan increase in the level of integration. Also, with smaller and smallerstructures, increasing demands are placed on structure production. Tomeet these demands, greater resolution or higher contrast is required ofthe applied photoresists.

When photoresists are structured using photolithographic means, inaddition to the technology- and resist-specific parameters, theproperties of the stepper or the stepper lens used for irradiation alsodetermine the minimum attainable structure size, critical dimension(CD), as well as the depth of focus (DOF). The stepper-specificvariables, exposure wavelength λ and lens numerical aperture (NA), arerelated to CD and the DOF as follows:

CD=f₁ (λ/NA) and DOF=±f₂ (λ/NA²); wherein f₁ and f₂ are factors whichare specific to the processing equipment.

For some time, the demands of photolithography have been satisfied byliquid-developable single-layer resists, particularly those consistingof novolak resins (as a base polymer) and quinone diazides (as aphotoactive component). Such resist systems, however, may be unable tomeet future requirements. For example, when thick resists are processedusing excimer laser steppers in the deep-ultra-violet (DUV) range, itmay be impossible to produce relief structures having steep edges anddimensions of less than 0.5 μm. This is particularly true of graduatedsubstrate topographies and highly reflective sub-layers. To produce verysmall structures, shorter exposure wavelengths and high numericalapertures are needed. Unfortunately, this reduces the range of the depthof focus, making it very difficult to use liquid-developablesingle-layer resists (with relatively thick resist layers andunavoidable fluctuations in layer thickness) when high resolution ongraduated topographies is required. In addition, these systems are notsuited for application as DUV resists, particularly due to the highself-absorption of novolak, for example, at 248 nm.

To eliminate the problems associated with the application ofliquid-developable single-layer resists, so-called two-layer systemswere developed. These systems, however, are more complicated. In thetwo-layer systems, a single thin upper layer is irradiated andstructured (i.e., developed or chemically modified through treatmentwith an agent). The structure produced in the upper layer serves as acontact mask and is subsequently transferred to the lower layer(s). Tostructure the lower layer, UV-light provided by a flood exposure (i.e.,irradiation without an overlay mask) can be used in conjunction withliquid-development or with dry-development techniques such as reactiveion etching in an oxygen plasma (O₂ /RIE).

Dry-developable single-layer systems have the advantages of thetwo-layer systems, while being less complex. In these systems, a latentimage is produced through the irradiation of the surface of a resistlayer that has been deposited on the substrate. The resist is thentreated with a metal-containing organic reagent (e.g., an organosiliconcompound) whereby, depending on the type of process control desired,either only the exposed areas (negative resist) or only the unexposedareas (positive resist) react with the reagent. The non-silylated areasare then dry-developed by etching in an oxygen plasma.

One problem with DUV lithography is that the sensitivity of resistscontaining quinone diazides or aliphatic diazoketones as photoactivecomponents is low and does not meet production demands. To increasesensitivity, particularly in DUV lithography, systems have beendeveloped which work according to the so-called "chemical amplificationprinciple". These systems are applicable to both wet-developable resistsand dry-developable resists. European Published Patent Application 0 102450 is related to wet-development; European Published PatentApplications 0 161 476 and 0 229 917 are related to dry-development.

In contrast to conventional diazoketone/novolak systems, these systemsconsist, for example, of tertiary butoxycarbonyloxystyrol (as a basepolymer) and of a so-called "photo-acid generator" (as a photoactivecomponent). The photo-acid generator is a compound which forms a strongacid during exposure; the polarity of the base polymer also changesafter exposure. Moreover, each acid molecule splits several protectivegroups. This fact is a characteristic feature of the chemicalamplification and leads to high sensitivities. Additional possibilitiesof chemical amplification exist for systems besides those having Bocgroups (Boc=tertbutoxycarbonyl). For example, one can also applycleavable ethers as protective groups for acid-catalyzed splitting.

European Published Patent Application 0 161 476 discloses a resistconsisting of tert-butoxycarbonyloxystyrol and a photoactive componentin the form of triphenylsulphoniumhexafluoroarsenate. This resist isirradiated with UV light through an overlay mask and treated in a vacuumoven for one hour at 85° C. with gaseous hexamethyldisilazane (HMDS),thereby silylating the exposed areas of the resist surface. Afterreactive ion etching in an oxygen plasma and treatment with diluted,buffered hydrofluoric acid, highly resolved, negative structures withvertical edges are obtained. Trimethylsilylchloride and trimethyl-tinchloride are possible treatment reagents in addition tohexamethyldisilazane. The treatment reagents should be applicable in thegas phase or in a "suitable solvent". More detailed specifications,however, are not to be found.

European Published Patent Application 0 192 078 discloses a method forproducing negative resist structures using a dry-developable resistsystem. First a base polymer containing a cationic photoinitiator,particularly a triarylsulphonium salt or a trihalogenatedmethyltriazine, is applied to a substrate. After exposure, the resistlayer is treated with a cationically polymerizable monomer to form apolymer film. This film protects the exposed areas during the subsequentplasma etching. The treatment with the monomer is preferably conductedusing an epoxysiloxane or -silane, or a styrolsilylether. These reagentscan be applied in the gas phase or in solution.

A dry-developable negative resist system which works according to thechemical amplification principle is also known. Here, silylation withHMDS takes place after a Boc protective group is split (c.f., SPIE's1990 Symposium on Microlithography, Mar. 4-9, 1990, San Jose, Calif.:Volume of Minutes, page 101). To produce positive resist structures,European Published Patent Application 0 229 917 discloses treating theexposed resist with a non-metalorganic compound in the form of anisocyanate. After a flood exposure (i.e., after an exposure without anoverlay mask), the resist is treated with a metalorganic reagent in theform of a tin or silicon compound, such as HMDS. Finally, the resist isdry-developed (see also, European Published Patent Application 0 251241).

The above-mentioned systems however, have the following disadvantages:use of moisture-sensitive, corrosive, poisonous or at the very leasthealth-threatening gases or organic solvents; requirement for specialvacuum apparatus; treatment at elevated temperatures; and complicatedprocess control with difficult reproducibility.

European Published Patent Application 0 394 740 proposes a negativeworking, dry-developable resist system which, contrary to comparablesystems, permits easy handling, features a high selectivity in theoxygen plasma, leads to highly resolved structures with steep edges, andfinds application in existing customary apparatus. A characteristicfeature of this system is that the resist is treated with ametal-containing organic reagent in an aqueous or water-containing,non-toxic phase, and it is implemented under ambient conditions (i.e.,at room temperature and standard pressure). This resist system, whichconsists of a base polymer with reactive groups (e.g., a copolymer ofstyrol and maleic anhydride) and a photoactive component based onquinone diazide, works according to conventional principles. In otherwords, during irradiation, when a carboxylic acid is formed from thequinone diazide, only the polarity of the photoactive component ischanged. For this reason the proposed resist system is relativelyinsensitive with currently available devices, particularly forapplications in DUV lithography.

SUMMARY OF THE INVENTION

The present invention describes a method for producing high resolutionresist structures with steep edges and a dry-developable resist systemsuited for this method.

Besides permitting ease of operation, the present invention has highoxygen plasma selectivity, is applicable to existing standard equipment,and has high sensitivity, particularly in the DUV range.

In the present invention, a photoresist layer comprising a polymer and aphotoactive component are deposited on a substrate. The photoactivecomponent is in the form of a compound which forms a strong acid duringirradiation; the polymer contains anhydride groups and blocked imide orphenolic hydroxyl groups. This photoresist layer then is irradiated witha patterned image, followed by treatment with a water-based or awater-alcohol-based solution of a polyfunctional amino- orhydroxy-siloxane. The photoresist layer treated in this manner is thenetched in an oxygen-containing plasma.

More specifically, the present invention, which works according to thechemical amplification principle, generally comprises the followingsteps:

A resist consisting of a base polymer and a photoactive component isapplied to a substrate, for example, a silicon wafer. The resist istypically applied in the form of a solution, which may containadditives, such as sensitizers. The base polymer contains chemicallyreactive groups in the form of anhydride groups, but it is neverthelessstable in storage. Compounds which form a strong acid during irradiationserve as photoactive components; onium salts and halogen-containingtriazine derivatives are preferable compounds.

In addition to the anhydride groups, the base polymer contains blockedfunctional groups, specifically in the form of imide groups or phenolic--OH groups. A Boc group, for example, can be used to block (i.e.,protect) these groups. However, phenolic -OH groups can also beprotected or blocked by acid-cleavable ethers. It is believed that theacid produced from the photoactive component during irradiationcatalytically splits the protective groups allowing the functionalgroups (i.e., imide- or phenolic OH groups) to be released. It is alsobelieved that these functional groups then make it possible for theamino- or hydroxy-siloxane to be selectively incorporated, i.e., itsdiffusion into the photoresist layer and a reaction with the anhydridegroups of the base polymer.

Suitable base polymers are, for example, copolymers oftert-butoxycarbonyloxystyrol and maleic anhydride or terpolymers oftert-butoxycarbonyloxystyrol, maleic anhydride and styrol.Acid-cleavable ethers of p-hydroxystyrol such as isopropyl- andtert-butyl-ethers also come under consideration as comonomers for maleicanhydride. Base polymers with blocked imide groups include terpolymersof maleic anhydride, styrol and maleinimide that is blocked, for examplewith a Boc protective group).

The method of the present invention can also be conducted by applying apolymer featuring only anhydride groups. In this case, additives havingblocked functional groups (i.e., hydroxyl groups) are then added to thepolymer. These additives, which produce -OH groups in the presence ofacid (i.e., in the exposed areas), block the silylation of the anhydridegroups in the unexposed areas. The blocked --OH groups can exist in theform of acetal-, ketal- or orthoester-groups The hydroxyl groups canalso be phenolic --OH groups which are then blocked in the mannerindicated above. For this purpose, tert-butoxyphenyl- andtert-butoxycarbonyloxyphenyl- groups can be used. Suitable polymers are,for example, copolymers of maleic anhydride and styrol. EuropeanPublished Patent Application 0 394 740 specifies several other suitedpolymers.

After the resist solution is applied to the substrate, it is dried,followed by irradiation through an overlay mask. After the exposure, theresist layer is preferably subjected to a temperature treatment usingstandard equipment before it is treated with a solution of apolyfunctional amino- or hydroxy-siloxane. Such organosilicon compoundsare preferably diaminosiloxanes. Suitable compounds are described in theEuropean Published Patent Application 0 394 740. The organosiliconcompounds are applied in form of solutions, i.e. as water-basedsolutions or water-alcohol-based solutions, wherein isopropanol isparticularly suitable. After treatment with the organosilicon compound,dry development is conducted in an oxygen plasma (O₂ /RIE).

The procedure described above produces negative resist structures.However, the method of the present invention can also be used to producepositive resist structures. For this purpose, after exposure ortemperature treatment (i.e.. before treatment with the organosiliconcompound), the photoresist layer is treated with a polyfunctionalorganic compound having functional groups that can chemically react withthe anhydride groups of the polymer.

It is believed that treatment with the polyfunctional organic compoundcauses the base polymer to be blocked in the exposed areas. Thistreatment step is followed by a flood exposure. During subsequenttreatment with the organosilicon compound, only the flood-exposed areasreact. These are the only areas protected from the plasma etching.Before the flood exposure, the resist can be subjected to a temperaturetreatment where it is tempered for a short time (e.g. 90 seconds) attemperatures in the range of 100° C. (e.g., 110° C.). After the floodexposure, the resist is treated with the organosilicon compound,followed by plasma etching.

A polyfunctional, organic compound, which is preferably metal-free, maybe used with the method of the present invention. This compound is apolyamine with at least two amino groups; aliphatic polyamines or evenamines with aromatic partial structures are preferably used. Suitablepolyfunctional amines are, for example, triethylene tetramine,tetraethylene pentamine, tris(2-aminoethyl)amine,N,N'-bis(3-aminopropyl)-1,2-ethylenediamine and3-(aminomethyl)benzylamine. These compounds, which serve ascross-linking reagents, can be applied in the form of aqueous solutions.

In addition to single-layer systems, the invention can be applied indry-development two-layer systems. In two-layer systems, the reactiveresist is applied as a thin layer to a dry-etchable planarization layerwhich can be freely selected according to the requirements at hand.Generally, semiconductor material, metal, ceramic, or the like is usedas a base, i.e., as a substrate.

DETAILED DESCRIPTION

The invention is explained in greater detail based on the followingexamples. The starting materials or treatment reagents that are used inthe examples are:

Base polymer (1): A copolymer of maleic anhydride and4-(tert-butoxycarbonyloxy)-styrol which is prepared through the radicalpolymerization of the two monomers. Azoisobutyric-acid nitrile is usedas an initiator and an alkylmercaptan is used as a regulator.

Base polymer (2): A copolymer of maleic anhydride and4-(tert-butoxycarbonyloxy)-stryol which is prepared through the radicalpolymerization of the two monomers using azoisobutyric-acid nitrile asan initiator (without regulator).

Base polymer (3): A copolymer of maleic anhydride and4-(tert-butoxy)-styrol which is prepared through the radicalpolymerization of the two monomers. Azoisobutyric-acid nitrile is usedas an initiator and an alkylmercaptan is used as a regulator.

Base polymer (4): A terpolymer of maleic anhydride,4-(tert-butoxycarbonyloxy)-styrol and styrol, prepared through theradical polymerization of the three monomers with azoisobutyric-acidnitrile as an initiator and an alkylmercaptan as a regulator.

Base polymer (5): A copolymer of maleic anhydride and styrol, preparedthrough the radical polymerization of the two monomers withazoisobutyric-acid nitrile as an initiator and an alkylmercaptan as aregulator.

Photoactive component (1): A compound which forms a strong acid duringexposure. Suitable acid producers include onium compounds known ascrivello salts and triazine derivatives; bis[4-(diphenylsulphonium)-phenyl]-sulphide-bis hexafluoroantimonate isused.

Additive (1): A compound from which at least one hydroxyl group isliberated by means of a strong acid;4-(tert-butoxycarbonyloxy)-diphenylmethane is used.

Silylation solution (1): A water-alcohol solution consisting of 4 partsby weight of diaminosiloxane, 82.3 parts by weight of isopropanol and13.7 parts by weight of water. The diaminosiloxane is preferably anδ,ω--aminofunctional siloxane, particularly one with two terminalaminopropyl groups and 2 to 20 silicon atoms in the chain. A commercialproduct, Tegomer A-Si 2120 (firm Goldschmidt), is used.

Silylation solution (2): A water-alcohol solution comprising 2 parts byweight diaminosiloxane (Tegomer A-Si 2120), 78.4 parts by weightisopropanol and 19.6 parts by weight water.

Silylation solution (3): A water-alcohol solution comprising 1 part byweight diaminosiloxane (Tegomer A-Si 2120), 79.2 parts by weightisopropanol and 19.8 parts by weight water.

Cross-linking solution (1): An aqueous solution comprising 2 parts byweight of tris(2-aminoethyl)-amine and 98 parts by weight water.

EXAMPLE 1

A resist consisting of 17.1 parts by weight of base polymer (2), 0.9parts by weight of photoactive component (1) and 82 parts by weight ofcyclohexanone is centrifuged on to a silicon wafer (2500 rpm, 20seconds). After drying at 100° C. for 60 seconds on a hot plate, thethickness of this resist layer is 1.1 μm. The resist is thencontact-printed through an overlay mask with 15 mJ/cm² (unit MJB 3 /Karl Suss: λ=250 nm), tempered for 60 seconds at 110° C., treated for 30seconds with silylation solution (1) and rinsed for 30 seconds withisopropanol. The silicon wafer is subsequently placed in aplasma-etching installation (Material Research Corporation, type MIE720) and the resist dry-developed in an oxygen plasma (O₂ /RIE: 2 mTorrgas pressure, 50 V bias voltage, with magnet). Negative structures withvertical edges are obtained with dimensions down to 0.3 μm.

EXAMPLE 2

The commercial positive resist TSMR 8900 (firm Tokyo Ohka Kogyo Co.) iscentrifuged onto a silicon wafer (4000 rpm, 20 seconds) and dried for 5min. at 90° C. The resist is then baked out for 35 minutes in a forcedair oven at 240° C. After baking, the thickness of the resist is 1.3 μmit is used as a planarization layer.

A resist consisting of 15.2 parts by weight of base polymer (1), 0.8parts by weight of photoactive component (1) and 84 parts by weight ofcyclohexanone is centrifuged onto the planarization layer (4500 rpm, 20seconds). After drying at 100° C. for 60 seconds on a hot plate, thelayer thickness of this top resist is 440 nm. The resist is thencontact-printed through an overlay mask with 13 mJ/cm² (unit MJB 3/ KarlSuss: λ=250 nm), tempered for 60 seconds at 110° C., treated for 30seconds with silylation solution (1), and rinsed for 30 seconds withisopropanol. The silicon wafer is subsequently placed in aplasma-etching installation (Leybold Heraeus, type Z 401) and the resistdry-developed in an oxygen plasma (O₂ /RIE: 6 mTorr gas pressure, 500 Vbias voltage). Negative structures with vertical edges are obtained witha line space ratio of 1:1 and dimensions of down to 0.3 μm.

EXAMPLE 3

A resist consisting of 14.9 parts by weight of base polymer (3), 1.1parts by weight of photoactive component (1), and 84 parts by weight ofcyclohexanone is centrifuged onto a planarization layer according toexample 2 (3000 rpm, 20 seconds). After drying at 100° C. for 60 secondson a hot plate, the layer thickness of this top resist is 400 nm. Theresist is then contact-printed through an overlay mask with 13 mJ/cm²(unit MJB 3/ Karl Suss: λ=250 nm), tempered for 60 seconds at 110° C.,treated for 45 seconds with silylation solution (2), and rinsed for 30seconds with isopropanol. After dry development (O₂ /RIE: 2 mTorr gaspressure, 50 V bias voltage, with magnet) in a plasma-etchinginstallation (Material Research Corporation, type MIE 720), wellresolved negative structures with steep edges are obtained withdimensions of down to 0.3 μ m.

EXAMPLE 4

A resist comprising 20.9 parts by weight of base polymer (4), 1.1 partsby weight of photoactive component (1), and 78 parts by weight ofcyclohexanone is centrifuged on to a silicon wafer (3000 rpm, 20seconds). After drying at 100° C. for 60 seconds on a hot plate, thelayer thickness of this resist is 1.2 μm. The resist is thencontact-printed through an overlay mask with 14 mJ/cm² (unit MJB 3/ KarlSuss: λ=250 nm), tempered for 75 seconds at 110° C., treated for 60seconds with the silylation solution (3), and rinsed for 30 seconds withisopropanol. The silicon wafer is subsequently placed in aplasma-etching installation (Material Research Corporation, type MIE720) and the resist dry-developed in an oxygen plasma (O₂ /RIE: 2 mTorrgas pressure, 50 V bias voltage, with magnet). Negative structures withdimensions down to 0.35 μm are obtained with steep edges and aline/space ration of 1:1.

EXAMPLE 5

A resist according to Example 2 is deposited in the described manneronto the base, dried, contact-printed through an overlay mask with 8mJ/cm² (unit MJB 3 / Karl Suss: λ=50 nm) and tempered for 75 seconds at110° C. The resist layer is subsequently treated for 60 seconds with thecross-linking solution (1), rinsed for 30 seconds with water, andtempered for 90 seconds at 110° C. As a result of this process, theexposed areas are so severely cross-linked that no silylation of theseareas takes place during subsequent treatment with the organosiliconcompound.

After a DUV flood exposure (without overlay mask) of 12 mJ/cm², theresist is tempered for 30 seconds at 100° C., treated for 35 secondswith silylation solution (1), and rinsed for 30 seconds withisopropanol. It is subsequently dry-developed in a plasma-etchinginstallation (Leybold Heraeus, type Z 401) with an oxygen plasma (O₂/RIE: 6 mTorr gas pressure, 450 V bias voltage). Positive structures areobtained with vertical edges and a line/space ratio of 1:1.

EXAMPLE 6

A resist consisting of 9.7 parts by weight of base polymer (5), 4.5parts by weight of additive (1), 0.8 parts by weight of photoactivecomponent (1), and 85 parts by weight of cyclohexanone is centrifugedonto a planarization layer according to Example 2 (4500 rpm, 20seconds). After drying at 90° C. for 60 seconds on a hot plate, thelayer thickness of this top resist is 300 nm. The resist is thencontact-printed through an overlay mask with 16 mJ/cm² (unit MJB 3/ KarlSuss: λ=250 nm), tempered for 60 seconds at 110° C., treated for 30seconds with the silylation solution (2), and rinsed for 30 seconds withisopropanol. After dry development (O₂ /RIE: 6 mTorr gas pressure, 500 Vbias voltage) in a plasma-etching installation (Leybold Heraeus, type Z401), negative structures with vertical edges are obtained havingdimensions down to 0.3 μm.

What is claimed is:
 1. A method for producing high resolution resiststructures with steep edges, comprising the steps of:applying to asubstrate a photoresist layer comprising a polymer having anhydridegroups and groups selected from the group consisting of blocked imide-and blocked phenolic hydroxyl groups, and a photoactive component whichforms a strong acid during irradiation; irradiating the appliedphotoresist layer with a patterned image; treating the irradiatedphotoresist layer with a water-based or water-alcohol-based solution ofa polyfunctional amino-siloxane or a polyfunctional hydroxy-siloxane;and etching the treated photoresist layer in an oxygen-containingplasma.
 2. The method according to claim 1 further comprising the stepof:subjecting the photoresist layer to an elevated temperature after thestem of irradiating the applied photoresist layer with a patternedimage.
 3. The method according to claim 5, wherein the photoactivecomponent is selected from the group consisting of an onium salt and ahalogen-containing triazine derivative.
 4. The method according to claim2, wherein after the step of subjecting the photoresist layer to atemperature treatment, the method further comprises the stepsof:treating the photoresist layer with a polyfunctional organic compoundhaving functional groups having a chemical reaction with the anhydridegroups of the polymer in the irradiated areas; and exposing thephotoresist layer to a flood exposure.
 5. The method according to claim4 further comprising the step of subjecting the photoresist layer to anelevated temperature before the step of exposing the photoresist layerto a flood exposure.
 6. The method according to claim 1, wherein afterthe step of irradiating the applied photoresist layer with a patternedimage, the method further comprises the steps of:treating thephotoresist layer with a polyfunctional organic compound havingfunctional groups having a chemical reaction with the anhydride groupsof the polymer in the irradiated areas; and exposing the photoresistlayer to a flood exposure.
 7. The method according to claim 6 furthercomprising the step of subjecting the photoresist layer to an elevatedtemperature before the step of exposing the photoresist layer to a floodexposure.
 8. The method according to claim 6, wherein the polyfunctionalorganic compound is a polyamine.
 9. The method according to claim 8,wherein the polyamine is an aliphatic polyamine.
 10. The methodaccording to claim 1, wherein the substrate is a dry-etchableplanarization layer.
 11. A method for producing high resolution resiststructures with steep edges, comprising the steps of:applying to asubstrate a photoresist layer comprising a polymer having anhydridegroups, an additive to the polymer having blocked hydroxyl groups, and aphotoactive component which forms a strong acid during irradiation;irradiating the applied photoresist layer with a patterned image;treating the irradiated photoresist layer with a solution of apolyfunctional amino-siloxane or a polyfunctional hydroxy-siloxane, thesolution being based on a solvent selected from the group consisting ofwater and water-alcohol mixtures; and etching the treated photoresistlayer in an oxygen-containing plasma.
 12. The method according to claim11 further comprising the step of:subjecting the photoresist layer to anelevated temperature after the step of irradiating the appliedphotoresist layer with a patterned image.
 13. The method according toclaim 4, wherein the photoactive component is selected from the groupconsisting of an onium slat and a halogen-containing triazinederivative.
 14. The method according to claim 12, wherein after the stepof subjecting the photoresist layer to a temperature treatment, themethod further comprises the steps of:treating the photoresist layerwith a polyfunctional organic compound having functional groups having achemical reaction with the anhydride groups of the polymer in theirradiated areas; and exposing the photoresist layer to a floodexposure.
 15. The method according to claim 14 further comprising thestep of subjecting the photoresist layer to an elevated temperaturebefore the step of exposing the photoresist layer to a flood exposure.16. The method according to claim 11, wherein after the step ofirradiating the applied photoresist layer with a patterned image, themethod further comprises the steps of:treating the photoresist layerwith a polyfunctional organic compound having functional groups having achemical reaction with the anhydride groups of the polymer in theirradiated areas; and exposing the photoresist layer to a floodexposure.
 17. The method according to claim 16 further comprising thestep of subjecting the photoresist layer to an elevated temperaturebefore the step of exposing the photoresist layer to a flood exposure.18. The method according to claim 16, wherein the polyfunctional organiccompound is a polyamine.
 19. The method according to claim 18, whereinthe polyamine is an aliphatic polyamine.
 20. The method according toclaim 11, wherein the substrate is a dry-etchable planarization layer.